There are many types of electronic systems powered by AC to direct current (DC) adapters including, printers, scanners, liquid crystal display (LCD) monitors, personal computer (PC) speakers, digital subscriber line (DSL) modems, etc. There are also many types of portable electronic systems that may be powered by either internal batteries or AC adapters, such as cellular phones, digital cameras, compact disc (CD) players, portable computers, and pocket computers.
There is a substantial likelihood that an adapter designed for one system having a particular voltage level may be accidentally plugged into another system with a different voltage level. An adapter with a high voltage level or a reversed polarity connector could cause severe damage if it is used to power a non-compatible host system. In certain cases, it may also result in safety hazards to a user.
Many prior art protection circuits that were designed to prevent powering a system with an incompatible adapter used a myriad of discrete components including diodes, fuses, zener diodes, and solid-state relays to provide a system protection from receiving power from incompatible voltage levels or voltage polarities. In addition, most prior art protection schemes lacked reliable anti-bounce circuitry. Intermittent contact or bouncing contacts during the initial plug-in period often leads to false triggering of the protection circuitry. Furthermore, the prior art protection schemes generally do not provide a proper interface that prevents a host system from being coupled to an adapter with incompatible voltage levels or polarities. The prior protection devices or circuits simply disable or electrically disconnect the adapter from the host system. A system user is not informed that they are using an incompatible type of adapter. There is, therefore, a need for an active protection device that can inform the host system in the event a user plugs an incompatible AC adapter into the system.